Recently, the demand for titanium alloys has greatly increased due to recent increases in fields in which they can be used, not only in the aircraft industry, but also in the field of consumer use. In particular, since high quality and various properties are required in alloys for aircraft use, high quality is the most important criterion, and in many cases, production cost reduction is secondary.
However, efforts to reduce production cost for titanium alloys would result in the increase of the amount used of light titanium alloys from a viewpoint of energy conservation of production processes of alloys and improvements in yields, that is, it would result in energy load reduction of operation of machines, and they would be considered to satisfying the needs of society.
In particular, Ti-6Al-4V alloy (hereinafter simply referred to as 64 alloy) has been conventionally used in the aircraft industry since it has superior mechanical properties. However, there is a problem in that the 64 alloy is difficult to assemble in parts having complicated structure because it has inferior workability.
In view of such circumstances, Ti-4.5Al-3V-2Fe-2Mo alloy (so called “SP700”) has been developed in order to improve workability of the 64 alloy. Furthermore, Ti-10V-2Fe-3Al (so called “10-2-3 alloy”), Ti-15V-3Cr-3Al-3Sn (so called “15-3-3-3 alloy”) or the similar alloy has been developed in which strength is further improved while maintaining the 64 alloy elongation level. However, vanadium or iron is easily segregated in any of the alloys SP700, 10-2-3, 15-3-3-3, and therefore further improvement has been required.
Under such circumstances, alloys having new compositions have been developed in order to prevent elements added from being segregated during production of the ingot, while maintaining the effect of the elements added in SP700, 10-2-3, or 15-3-3-3, at the same level or more, such as Ti-5V-5Mo-3Cr alloy (so called “5-5-5-3 alloy”), Ti-5Al-2Fe-3Mo alloy (so called “TiX-523 alloy”), and Ti-5Al-4V-0.6Mo-0.4Fe alloy (so-called “Timetal54M alloy”). It is considered that these new composition alloys aim to maintain effects of the alloy elements added at the same level or more as an overall alloy, by containing molybdenum and chromium instead of reducing vanadium and iron which are easily segregated elements. Problems of segregation have been solved to some extent by the development of these new alloys; however, segregation of alloy elements during solidification is inevitable even in these new composition alloys.
A technique has been known in which the 64 alloy is produced by a powder metallurgy using metallic powder as a raw material in order to prevent the elements added from being segregated during production of ingots. In the case in which it is produced by the powder metallurgy, a powder mixture consisting of pure titanium powder and alloy element powder, or a powder mixture consisting of pure titanium powder and master alloy powder of element added seems to be typically used as a raw material (see below Patent Document 1 and Non-patent Document 1).    Patent document 1: Japanese Unexamined Patent Application Publication No. Hei05 (1993)-009630    Non-patent document 1: Toyota Central Institute R&D Review Vol. 29 (1994), (3), pp. 49-60, by Saito and Furuta
These methods are called “blended elemental method”, and they are technically established. However, in the blended elemental method, although sintered material having high quality can be obtained, costs are high, and it is limited in practical use.
Reasons for high costs in the blended elemental method are that titanium powder is expensive due to the expensive pure titanium material used therein and the master alloy powder is also more expensive than pure titanium powder. Therefore, reduction in cost has been required. Furthermore, titanium alloy which is produced by the blended elemental method is consolidated by a method called HIP (hot isostatic pressing) in many cases, this method also results in increased cost, and a method is required in which titanium alloy can be produced at lower cost. As is described, a method is required in which titanium alloy, such as 64 alloy, can be produced at lower cost.